1. Field of the Invention
The present invention relates to the reception and preprocessing of digital messages available on at least one reception channel of a digital bus with a view to their use by a handling processor.
2. Discussion of the Background
It applies in particular, but not exclusively, to digital transmissions via digital buses such as those which are encountered on board aircraft for interconnecting the various on-board electronics. In the scope of these digital transmissions, each equipment item connected to a digital bus needs to select, from the messages in transit on the bus, those which are intended for it and extract the useful information items from these messages. For this purpose, the equipment item comprises a hardware reception device capable of intercepting the messages travelling on the bus, identifying the useful messages from among the intercepted messages and putting the collected useful messages in a memory area accessible to its processing and computation components, these components being generally in the form of a processor driven by software.
In order to permit the selection of the messages in transit on a bus by the right equipment items, it is known to provide each message with a label or tag explicitly or implicitly giving its destination equipment item or items.
The tag explicitly gives the destination or destinations of the message when it is formed by one or more addresses of equipment on the bus. This explicit mode of addressing the messages at the drawback of requiring, in the equipment item giving rise to the transmission of a message, prior knowledge of the addresses on the bus of all the other equipment items liable to be concerned by the message.
In order to avoid this drawback, which makes it necessary to intervene on the equipment items already in place on a digital bus each time a new equipment item is added, it is preferable to indicate, in the label or tag of a message, its destination equipment item or items implicitly by using the tag or label as an identifier of the message. Each equipment item connected to the digital bus analyses the tags of the messages in transit on the digital bus in order to identify their nature and select those which concern them.
In the case in which the transmitted messages contain an identification tag, it is fairly common for this tag to describe not only the nature of the message but also the type of the first processing operation or preprocessing operation to be applied to the message upon its reception, in particular in order to modify the format under which it travels on the digital bus, which depends on the protocol adopted for the transmission, into a format assimilable by the processor of the destination equipment item. This is because the possible uses of a message are often well known to the equipment item which is sending them, and it is in this way possible to accompany the message by preprocessing directions which relieve the input circuits of the destination equipment items of decision-taking operations which are expensive in terms of computation time. All the more so since these preprocessing decisions need to be taken very early in a destination equipment item, at the interface which manages the protocol of the reception channel or channels of the transmission bus. The reason is that this interface is very often formed, for reasons of universality (possibilities of using the same equipment item with various sorts of digital buses employing varied protocols), by a specialized machine with low processing capacity.
Usually, when a message travelling on a digital bus contains an identification tag with a preprocessing direction, the information content of the tag corresponds to a preprocessing program identifier with an address of the identified preprocessing program in the program memory or memories of the destination equipment items, given explicitly or implicitly, and optionally parameters associated with the identified preprocessing function. When such a message, in transit on a digital bus, is observed by an equipment item, the latter identifies the identification tag and analyses its content in order to ascertain whether it corresponds to a locally available preprocessing program. If this is so, the equipment item in question will look for the relevant preprocessing program in its memory and runs it. If this is not so, the equipment item ignores the message and waits for the next one.
Many examples of transmission systems using messages with identification tags having a preprocessing direction are found in the prior art, such as, for example, those described in the American Patent U.S. Pat. No. 5,444,643, in the French Patent Application FR-A-2,724,742 or in the European Patent Applications EP-A-0 675 024 or EP-A-0 666 200.
The operations of preprocessing the messages reaching an equipment item via a reception channel of a digital bus are most of the time carried out by manipulating registers at the input of the equipment item, and the configuration of the registers which is best suited to the preprocessing of a message varies with the type of message. However, the transmission systems in the prior art at present, such as those disclosed by the documents above, prove to be fairly fixed in so far as they do not make it possible to modify with ease the configuration of a reception channel of the digital bus at the input of an equipment item. In fact, in order to modify this configuration, it is necessary to intervene on the equipment item itself, which in practice prohibits modifications during transmission of messages.
The object of the present invention is to overcome the above drawbacks and to allow dynamic modification of the configuration of a reception channel of a digital bus at the input of an equipment item.
For this purpose, it provides a method for the reception and preprocessing of digital messages available on at least one reception channel of a digital bus, with a view to their use by a handling processor for which the messages are intended, each message comprising useful information items and a tag identifying these useful information items.
This method comprises:
the association of the tag of each message capable of being received with a descriptor relating to operations to be had carried out by a handling processor for which the message in question is intended,
the storage of the descriptors in a memory at respective addresses calculated with the aid of the tags of the associated messages, and
upon reception of a message, the reading of the tag of the received message, the calculation of the descriptor""s address obtained with the aid of the tag, the reading in memory of the descriptor at the address thus calculated, and the running of the operations indicated by the descriptor.
According to the invention, the descriptors belong to various categories, including a category of preprocessing descriptors each containing all the parameters defining a preprocessing operation to be applied to the associated message, and a category of instruction descriptor corresponding to instructions to modify the control parameters of a reception channel, to an instruction for branching, conditional or unconditional, to another descriptor, to an instruction to compare the information items contained in the associated message with reference values or to an instruction to compare pointers for writing in data structures of the ring or frame type with reference values.
By virtue of these arrangements, the handling processor becomes entirely relieved of the selection of the operations of preprocessing the received messages, the definition of these operations being configurable and being capable of being modified dynamically by instruction sequences associated with certain messages, the running of which by a sequencer in charge of running the preprocessing operations is triggered by the reception of these messages. It is hence thus possible to produce operating modes which are more complex.
According to one feature of the invention, each sequence of instruction descriptors ends with a preprocessing descriptor.
According to another feature of the invention, each preprocessing descriptor comprises a memory address of a data block with predefined structure, in which the corresponding message is to be stored, this data block comprising a formatting information item defining more precisely the formatting operations to be applied to the message, so as to make the information items which it contains directly usable by a handling processor for which the message is intended, the application of the preprocessing operations defined by the message descriptor being followed by the application of the formatting operations to the useful information items of the message, and the storage of the information items thus formatted at predefined locations in the data block.
In this way, the message reception device is capable of relieving the handling processor of the sophisticated operations of formatting the received information items, and in an entirely configurable way by virtue of the use of a block of preloaded data comprising the precise definition of these formatting operations.
According to another feature of the invention, the handling processor is connected to a plurality of channels for transmitting digital messages, the method according to the invention furthermore comprising the association of each transmission channel with a channel control register indicating the address of the area containing the descriptors of the messages capable of being transmitted by this channel, as well as general parameters defining the preprocessing operations to be applied to these messages, the channel control registers being stored in memory at predefined respective addresses, the reception of a message by a channel triggering the reading of the control register of the channel, and the calculation of the address of the descriptor of the message with the aid of the tag of the message and the address of the area with the descriptors of the messages, which is read from the control register of the channel.
The invention also provides a device for carrying out the method according to the invention, this device comprising a sequencer machine designed to run the instruction sequences and the preprocessing operations on the received messages while taking into account the preprocessing parameters indicated by the corresponding descriptors.